[Patent document 1] JP 2000-348300 A
[Patent document 2] JP 2003-217074 A
To perform vehicles-convoy running, an apparatus for tracking running with the second and the subsequent vehicles with respect to a preceding vehicle has been proposed (e.g., see Patent documents 1 and 2). Patent document 1 discloses obtaining, from a different vehicle, tracking running data such as positional information, measured in the different vehicle of a vehicles convoy using a GPS apparatus, via inter-vehicle communication. Further, Patent document 1 discloses detecting a preceding vehicle with a laser radar and correcting the above-described tracking running data based on the result of detection. Further, Patent document 2 discloses using a wide area or local area radio communication device so as to deal with a trouble in the inter-vehicle communication device, via which data communication is made among respective vehicles of a vehicles convoy.
In Patent document 1, the result of detection using the laser radar is used in correction of the positional information measured with the GPS apparatus. When the GPS apparatus, in addition to the laser radar, is provided, it is possible to have plural distance measurement devices using these apparatuses respectively for measuring the distance with respect to a preceding vehicle. Accordingly, it is possible to select one of these distance measurement devices. That is, when it is impossible for one of these distance measurement devices to measure the distance to the preceding vehicle, the current distance measurement device can be replaced with the other distance measurement device.
For example, in the laser radar, as a detection angular range to detect the preceding vehicle is limited to a comparatively narrow angular range in a vehicle front position, there is a probability that it cannot detect the preceding vehicle at a tight curve in the road or the like. When the current detection device using the laser radar is replaced with the device to detect the distance to the preceding vehicle based on the position measured with the GPS apparatus, it is possible to reduce the time in which the result of measurement of distance to the preceding vehicle cannot be obtained to a great extent.
However, when the distance measurement device is selected, the following occurs. No matter what the measuring method is, the distance measurement device has a measurement error. Accordingly, when tracking running with respect to a preceding vehicle is performed, it is preferable to set a target inter-vehicle distance between the vehicle and the preceding vehicle in consideration of such measurement error. Further, the measurement error differs by type of distance measurement device. Accordingly, it is preferable that the target inter-vehicle distance differs in accordance with type of distance measurement device. When a long target inter-vehicle distance is set, as the influence of the measurement error on the target inter-vehicle distance is small, it is not always necessary to set the target inter-vehicle distance in accordance with type of distance measurement device. However, in the case of vehicles-convoy running, as the target inter-vehicle distance is often short, the measurement difference has a significant influence on the target inter-vehicle distance. Accordingly, it is necessary to set the target inter-vehicle distance in accordance with type of distance measurement device.
However, when the target inter-vehicle distance is immediately changed to a target inter-vehicle distance corresponding to the replaced distance measurement device, the speed radically changes in accordance with the radical change of the target inter-vehicle distance. This radical speed change may annoy the driver.